class ActiveSupport::MessageEncryptor

MessageEncryptor is a simple way to encrypt values which get stored somewhere you don't trust.

The cipher text and initialization vector are base64 encoded and returned to you.

This can be used in situations similar to the MessageVerifier, but where you don't want users to be able to determine the value of the payload.

salt  = SecureRandom.random_bytes(64)
key   = ActiveSupport::KeyGenerator.new('password').generate_key(salt) # => "\x89\xE0\x156\xAC..."
crypt = ActiveSupport::MessageEncryptor.new(key)                       # => #<ActiveSupport::MessageEncryptor ...>
encrypted_data = crypt.encrypt_and_sign('my secret data')              # => "NlFBTTMwOUV5UlA1QlNEN2xkY2d6eThYWWh..."
crypt.decrypt_and_verify(encrypted_data)                               # => "my secret data"

Constants

DEFAULT_CIPHER
OpenSSLCipherError

Public Class Methods

key_len(cipher = DEFAULT_CIPHER) click to toggle source

Given a cipher, returns the key length of the cipher to help generate the key of desired size

# File lib/active_support/message_encryptor.rb, line 70
def self.key_len(cipher = DEFAULT_CIPHER)
  OpenSSL::Cipher.new(cipher).key_len
end
new(secret, *signature_key_or_options) click to toggle source

Initialize a new MessageEncryptor. secret must be at least as long as the cipher key size. For the default 'aes-256-cbc' cipher, this is 256 bits. If you are using a user-entered secret, you can generate a suitable key by using ActiveSupport::KeyGenerator or a similar key derivation function.

Options:

  • :cipher - Cipher to use. Can be any cipher returned by OpenSSL::Cipher.ciphers. Default is 'aes-256-cbc'.

  • :digest - String of digest to use for signing. Default is SHA1.

  • :serializer - Object serializer to use. Default is Marshal.

# File lib/active_support/message_encryptor.rb, line 47
def initialize(secret, *signature_key_or_options)
  options = signature_key_or_options.extract_options!
  sign_secret = signature_key_or_options.first
  @secret = secret
  @sign_secret = sign_secret
  @cipher = options[:cipher] || 'aes-256-cbc'
  @verifier = MessageVerifier.new(@sign_secret || @secret, digest: options[:digest] || 'SHA1', serializer: NullSerializer)
  @serializer = options[:serializer] || Marshal
end

Public Instance Methods

decrypt_and_verify(value) click to toggle source

Decrypt and verify a message. We need to verify the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks.

# File lib/active_support/message_encryptor.rb, line 65
def decrypt_and_verify(value)
  _decrypt(verifier.verify(value))
end
encrypt_and_sign(value) click to toggle source

Encrypt and sign a message. We need to sign the message in order to avoid padding attacks. Reference: www.limited-entropy.com/padding-oracle-attacks.

# File lib/active_support/message_encryptor.rb, line 59
def encrypt_and_sign(value)
  verifier.generate(_encrypt(value))
end

Private Instance Methods

_decrypt(encrypted_message) click to toggle source
# File lib/active_support/message_encryptor.rb, line 90
def _decrypt(encrypted_message)
  cipher = new_cipher
  encrypted_data, iv = encrypted_message.split("--".freeze).map {|v| ::Base64.strict_decode64(v)}

  cipher.decrypt
  cipher.key = @secret
  cipher.iv  = iv

  decrypted_data = cipher.update(encrypted_data)
  decrypted_data << cipher.final

  @serializer.load(decrypted_data)
rescue OpenSSLCipherError, TypeError, ArgumentError
  raise InvalidMessage
end
_encrypt(value) click to toggle source
# File lib/active_support/message_encryptor.rb, line 76
def _encrypt(value)
  cipher = new_cipher
  cipher.encrypt
  cipher.key = @secret

  # Rely on OpenSSL for the initialization vector
  iv = cipher.random_iv

  encrypted_data = cipher.update(@serializer.dump(value))
  encrypted_data << cipher.final

  "#{::Base64.strict_encode64 encrypted_data}--#{::Base64.strict_encode64 iv}"
end
new_cipher() click to toggle source
# File lib/active_support/message_encryptor.rb, line 106
def new_cipher
  OpenSSL::Cipher.new(@cipher)
end
verifier() click to toggle source
# File lib/active_support/message_encryptor.rb, line 110
def verifier
  @verifier
end